Speaking to WCVB Channel 5's "On The Record" on Sunday, Coakley was asked how many cents per gallon the gas tax is. She guessed, "10 cents?" The correct answer is 24 cents.

Baker, in a statement, called Coakley "out of touch" and "uninformed" about the gas tax. "If you want to be Governor, and you support an automatic increase in the gas tax, you should know what the current tax rate is," Baker said. "That the Attorney General, who had to certify a ballot question on this topic, would think the state gas tax is 10 cents is a little scary."

Coakley spokeswoman Bonnie McGilpin responded, "Very few people get 100 percent of the pop quiz questions on ("On The Record") correct. Martha knows that the gas tax is a critical funding source to make the transportation infrastructure investments that are necessary to move Massachusetts forward."

The gas tax has been a hot topic in Massachusetts. An increase in the gas tax was passed last year as part of an attempt to increase funding for the state's transportation infrastructure. The tax will go up by 3 cents in August, and will then be "indexed" automatically so it will change in future years to match growth in the consumer price index.

A group of activists are collecting signatures to place a question on the ballot in November eliminating the indexing provision. As Massachusetts attorney general, Coakley was responsible for certifying the ballot question.

The organizers of the ballot campaign – State Rep. Geoff Diehl, a Whitman Republican, Steve Aylward and Marty Lamb – also sent out a statement attacking Coakley for her mistake and calling her "out of touch." "The gas tax has not been 10 cents per gallon since before I was born," Diehl said.